In ATM distribution systems, the physical layer is defined as a functional group comprised of hardware, software and transmission media which converts an ATM cell stream into bits to be transported over the transmission media and supports the transmission and reception of these bits. Examples of transmission media are optical fiber, coaxial cable, free space, and twisted copper pairs. Once the data is transported over the physical layer it is presented to the next layer, the Asynchronous Transmission Mode (ATM) layer. At the output of the device, the data can be presented via a number of interfaces, one of which is the Universal Test & Operations PHY Interface for ATM (UTOPIA) as described by the ATM Forum.
Simultaneously with the development of ATM technology, there have been advances in Fiber-to-the-Curb (FTTC) technology in which devices are connected to the telephone central office via a network of optical fibers connecting the central office to single network points called Broadband Network Units (BNUs) which in turn connect to the subscriber residence via a coaxial cable, and to the devices in the residence via a passive splitter and in-home coaxial wiring. In these FTTC networks, signals can be routed to the residence via a single coaxial cable connecting the residence to the BNU, but the passive network in the home results in information arriving at multiple devices, each which must have the ability to determine which signals are for that particular device. Likewise, when devices transmit from the residence to the BNU the BNU must have a mechanism for determining from which device the information was transmitted from.
When ATM transmission techniques are used, the information is in the form of cells which contain addressing which is known as the Virtual Path Identifier (VPI) and the Virtual Channel Identifier (VCI). The VPI and VCI fields can be read to determine the destination of a particular cell, but when a passive point-to-multipoint network which does not contain switching or routing capabilities is part of the physical layer cells destined for a particular device will arrive at multiple devices. Having the all receiving devices read all of the cells to determine which cells are actually destined for that device from their VPI/VCI values results in an inefficient means of cell discrimination and will require additional cell processing capability at each device. An additional problem arises in that in the reverse direction on the point-to-multipoint network the devices will transmit cells to a single receiving point, and that receiving point will not be able to determine from which originating device the cells were transmitted, without inspection of the VPI/VCI values.
One of the goals of the present invention is to provide one or more embodiments which permit the transport of ATM cells over a point-to-multipoint network, such as those encountered in FTTC.
Another goal of the present invention is to provide one or more embodiments which result in a physical layer in which the transceivers can be implemented in low cost monolithic integrated circuits which provide discrimination of cells such that the physical layer supports cells being transmitted over a point-to-multipoint network without examining the VPI/VCI fields within the cells.